Well treatment fluids are often aqueous gellant systems containing a viscoelastic surfactant. When thickened, such fluids may be useful in the control of fluid loss in gas or oil well drilling operations, as proppant carriers and as fluid loss control agents in well completion and workover operations.
Such gellant systems have particular applicability when used in fracturing fluids. Typically, the fracturing fluid is prepared on-the-fly, wherein the base media may be 65° F. or less. Fracturing of the formation is accomplished by pumping the fracturing fluid into the borehole of an oil or gas well under high pressure to create fractures in the rock formation surrounding the wellbore. The fractures radiate outwardly from the wellbore, typically from a few to hundreds of meters, and extend the surface area from which oil or gas drains into the well. Frequently, a proppant, whose function is to prevent the created fractures from closing back down upon itself when the pressure is released, is suspended in the fracturing fluid for transport into the fracture. The proppant filled fractures provide permeable channels allowing petroleum to seep through the fractures into the wellbore where it is pumped to the surface.
The fluid structure of the fracturing fluid should therefore be sufficiently viscous in order to suspend the proppant and to transport the proppant into the formation. In particular, the fracturing fluid should exhibit adequate viscosity prior to reaching the wellbore to ensure proppant placement, though viscosification may not be complete until the fluid reaches the formation.
A problem often encountered with viscoelastic based gellant systems is their inability to develop sufficient viscosity at temperatures lower than about 65° F. Thus, such systems are often ineffective in the transportation of proppants into the formation when the base media temperature is less than 65° F. Further, the temperature gradient is typically insufficient to cause viscosification of the fluid by the time it reaches the perforations. As a result, the efficiency of proppant transport into the formation is severely compromised.
Even in instances where viscosity of the well treatment fluid can be established for proppant transport, the time to effectuate the requisite gellation may be lengthy. In other instances, the cost of the viscoelastic surfactant used in the fracturing fluid may be high.
Alternatives have therefore been sought which will more effectively enhance the viscosity of viscoelastic surfactant containing well treatment fluids, including those fluids which contain a base media having a temperature of less than or equal to 65° F. Alternatives have further been sought which will decrease the time for gellation of viscoelastic surfactant-based well treatment fluids and/or provide a more cost effective alternative to the fluids presently used.